1. Field of the Invention
The invention relates to a limited extent to the field of variable clearance engines. However, because of additional novelty of the design and because of the additional complexity of the mechanism and its effect on piston motion, the invention may be classified more accurately as belonging to the field of advanced reciprocating engine systems. This latter classification refers to any engine system in which movement of the piston is not entirely dependent on the simple harmonic motion induced by rotation of the crankpin.
2. Description of Prior Art
In the conventional reciprocating engine system the connecting rod is a simple rigid link comprising an element of the four-bar linkage slider mechanism. The invention presented incorporates a pivot or hinging joint at some point near the center of the connecting rod and therefore the linkage network of this system becomes a five-bar mechanism. This introduces a certain amount of random movement in the linkage which must be controlled within definite limits if the mechanism is to be useful. In order to accomplish this the pivoting action is restricted in a manner such that the connecting rod longitudinal axis is straight in one position and hinged approximately 30.degree. in another position. These positions are referred to respectively in other parts of the specification as the uncocked and cocked positions. At intermediate transition points between these two positions the piston is free floating. Actuation from one to the other depends on the careful balance of total gas pressure forces operative at the piston face and transmitted along the connecting rod longitudinal axis, and the reactant resultant vector components of tangential and inertial forces centered at the crankpin and acting along the connecting rod longitudinal axis respectively. The linkage is therefore controlled in a manner such that during the compression stroke the rod is pivoted at the cocked angle of approximately 30.degree. while at the end of the exhaust stroke the connecting rod is in the fully extended straight or uncocked positon. Because piston travel is greater in the uncocked position the piston displaces more of the combustion gases in the clearance volume during the exhaust stroke. This decreases the amount of residual combustion gas in the clearance volume and therefore the subsequent inducted fresh fuel/air charge is not heated to the same extent thus improving the engine volumetric efficiency. Ignition is also improved since vitiation of the fresh charge is not as great which promotes the initial flame propagation at the lower dilution level.
There is another advantage to the system which is of a more subtle nature. During the initial expansion stroke the connecting rod is hinged in the 30.degree. cocked position. However, as the piston drops the angularity between the piston wrist pin and crankpin changes and gas pressure on the piston face is lower and the resultant vector dynamic forces cause the connecting rod to snap into the straightened or uncocked positon. The general effect on the engine is to cause the cylinder pressure to increase slightly during this period and thus obtain more power from the expansion stroke.